Anode-cathode construction for brain polarograph



L. R. PARTON Jan. 24, 1961 ANODE-CATHODE CONSTRUCTION FOR BRAIN POLAROGRAPH Filed May 18, 959

INVENTOR.

ATTORNEYS ANODE-CATHODE CONSTRUCTION FOR BRAIN POLAROGRAPH Lawrence R. Parton, 5458 Mitchell Drive, Dayton, Ohio Filed May 18, 1959, Ser. No. 814,119

1 Claim. (Cl. 1282.1)

(Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to an improved polarograph electrode assembly used in determining the oxygen availability or tension in the brain tissues of small animals under different environment conditions, or due to the effects of drugs or other factors.

The general procedures in making polarographic studies of oxygen availability in small animals is reported in an article by Clark, Wolf, Granger and Taylor, Journal of Applied Physiology, Vol. 6, page 189, 1953 and in Wright Air Development Center Technical Reports 57- 570 and 58-322 (1958), copies available from the Oifice of Technical Services Department of Commerce, which reports contain a complete bibliography of the pertinent medical literature.

From the work of the prior investigators it has been determined that if a constant voltage of the order of six tenths of a volt is applied in a circuit including a small wire cathode implanted in the brain tissue of a living small animal and an anode electrode implanted in the skin or muscle of the animal, the current flow from the anode to cathode is a measure of the availability of oxygen in the brain tissue.

When a small animal, such as a cat, has a fine wire cathode electrode implanted in its brain tissue and also provided with a suitable anode electrode, with a suitable direct current voltage applied across the electrodes such as from .4 to .9 volts, the applied voltage tends to depolarize the oxygen from the brain tissue collecting at the cathode and a current will flow. As the animals environment is changed, such as variation in the composition of the atmosphere breathed, atmospheric pressure and temperature, or drugs introduced into the animals bloodstream, the quantity of oxygen available, also called oxygen tension, in the brain tissue will vary. The variation in oxygen availability directly affects the flow of current between the anode and cathode electrodes and by using a recording galvanometer the change in current flow can be directly interpreted in terms of available oxygen.

In the prior art procedures it was necessary to make a large incision through the skin and muscular tissue overlying the skull of the small animal and to scrape the skull to obtain a considerable area which was tissue-free and dry. It was then necessary to trephine the skull for insertion of a glass-covered platinum wire having an exposed end which was implanted in the brain tissue. In order to retain the cathode in position it was further necessary to implant one or more anchoring screws in the animals skull in the prepared area and to fix the cathode in place by pouring an acrylic resin over the prepared site on the skull so as to secure the cathode in a fixed position, the screws serving as a means to anchor the hardened acrylic resin. It was further necessary to implant a silver anode in the incision already made or em I ICC

at some other position on the animals body. Due to the extensive surgery necessary and the relatively large mass of acrylic resin required to fix the cathode electrode in position great difliculties arose in finally getting a stable electrical condition. There is a strong tendency for the animal to try to dislodge the mass of acrylic resin mounted on its skull, and to retain the cathode electrode in an absolutely fixed position relative to thebrain tissue is very difiicult, if not impossible. Further, postoperative infections arising at the site of the implant or fixing'of both the anode and cathode electrodes further complicated the situation. Under ideal conditions some previous experimenters have been able to achieve very desirable results in measuring the oxygen availability in the brain tissue while the animal was placed in a changing environment, such as subjecting the animal to G forces in a centrifuge, varying the ambient atmospheric temperature and pressure to simulate conditions of altitude, or to administer drugs to the animal to measure the toxic effect thereof as reflected in the changed availability of oxygen in the brain tissues. While this general procedure ofiers a field for medical experimentation the surgical difiiculties, coupled with the dilficulty of getting reproducible results from one animal to the other due to variation in the positioning of the cathode, or other causes, has not caused this method to receive the attention that it otherwise deserves.

In accordance with the present invention the difficulties encountered with the prior art procedures have been obviated by greatly reducing the amount of surgery required; and constructing the anode in the form of a small silver or silver plated metallic body terminating in a threaded portion which can be screwed directly into a small hole trephined in the animals skull, having the diameter of the trephined hole equal to the root diameter of the threads on the anode whereby the anode cuts its own threads into the body structure of the skull to thereby securely anchor the same in. a rigid manner and fixed against any movement relative to the skull. The incision and surgery necessary for implanting the anode into the skull is very minor as compared to that required in the prior art procedures, and hence the possibilities of infection and necrosis of the bone structure are greatly reduced. Because of its small size the animal is generally not aware of the positioning of the anode on its skull and the possibility of the animal displacing the anode or creating infection by scratching with a paw is materially reduced. In addition the anode serves as a receptacle with a central aperture through which the cathode, a glass coated platinum wire, is positioned for entry into the brain tissues. The cathode is positively supported against any displacement, both longitudinally and radially, by means of a support received in the anode and its fixation into the brain tissue is much more secure against displacement than could be accomplished in prior art procedures. Further, the liability of short circuits through the brain tissue to any implanting screws and the like, as used in the prior art, has been entirely avoided.

For a more complete understanding of the invention reference is made to the appended drawings, in which Fig. 1 is a top plan view of the composite anode and cathode construction in accordance with the invention drawn to a scale of twice full size.

Fig. 2 is a cross sectional view taken on line 2-2 of Fig. 1;

Fig. 3 is a schematic circuit diagram of a polarograph with which the assembly of Figs. 1 and 2 is employed.

Referring now to Figs. 1 and 2, reference numeral 1 generally indicates the assembled anode-cathode conin length and having a circular base portion 3 of the order of three-quarters of an inch in diameter. Above the base portion 3 is a hexagonal portion 4 adapted to be engaged by the fingers or a suitable tool for screwing the assembly into the skull of a small animal. Below the base portion 3 there is a concentric cylindrical portion 5 which has a length. of the order of nine sixty-fourths of an inch and one-quarter of an inch in diameter which is externally threaded throughout its length as indicated at 6 so that it may be screwed through the bone structure of the skull of a small animal such as a cat. The anode 2 is provided with an enlarged central blind bore 8 forming a well or receptacle and is also provided with a central drilled passage 9 extending from the bore 8 through the stem portion 5. The bore 8 is provided with an annular insulating ring 10 which serves as a support for a cathode plug 12 which is pushed therein with a close fit and partially overlies the top of the insulating ring 10. The cathode plug 12 is made of metal and rests on an insulating plug 13 of initially soft acrylic resin material placed in the bottom of the bore 8 and interior of the insulating annular ring 10; The cathode supporting plug 12 has a platinum cathode 14 wire centrally secured and soldered therein, the cathode being covered by means of an insulating capillary glass tube fused thereto throughout the major portion of its length. The cathode wire 14 has two or three millimeters of its tip exposed. The cathode plug 12 is provided with a terminal screw 16 for connection of an electrical conductor thereto, and similarly the anode 2 has an electrical connection screw 18 secured therein. In general the cathode plug 12, insulating sleeve 10 and insulating plug 13 are assembled together with the cathode wire 14 attached to the cathode supporting plug 12. The bottom of this assembly is then coated with a fluid acrylic resin insulating material and inserted into the bore 8 of the anode 2. Set screws 20 in the anode block 2 then serve as a means for locking the cathode assembly in place and also permit its removal for replacement by another assembly.

In practice a small incision is made in the subcutaneous tissue over one of the dorsums of the skull overlying the cerebrums of a small animal, such 'as a cat, and laying bare a small area slightly larger than the diameter of the threaded stem 5 of the anode block 2. Using a dental drill a small pilot hole is drilled through the skull and a circular saw-type trephining drill provided with a pilot is then employed to trephine a hole through the skull having a diameter substantially equal to the root diam eter of the threads 6 on the extension 5 of the cathode block 2. The anode block 2 is then screwed directly into the skull with the base portion 3 in contact with the skin of the animal. After the anode block 2 has been secured the insulating sleeve 10, the cathode plug 12, with insulating plug 13 and cathode wire 14 are assembled and then pushed into the bore 8 of the anode block 2 and secured by set screws 20 as previously described above. The assembly is then complete.

Immediately after the surgery an X-ray is taken to insure that the cathode wire 11 which pierces and is implanted in the brain tissue has not become bent or displaced and the general position of the assembly relative to the brain tissue is noted. After a recuperating period of two to three days the anode and cathode assembly may be electrically connected to the brain polarograph for conducting the desired experiment.

As seen in Fig. 3 the anode-cathode assembly 1, Figs. 1 and 2 has the anode contact 18 connected by means of a conductor 25 to a potentiometer 26 which is used to adjust the voltage from a battery 27 in a range of from four to nine tenths of 21 volt as indicated on a voltmeter 28 shunted across the potentiometer 26. The other terminal of the potentiometer is connected by means of a conductor 29 in parallel to three resistances 30, 31. and 3.2 which have values of 9100, 18,000 and 36,000 ohms resistance respectively, which can be selectively switchedinto the circuit by means ofa three position switch 35, which is connected by means of conductor 36 to one side of a single pole double throw switch 38. The switch arm of switch 38 is connected by a conductor 40 to the cathode contact 16 of the anode-cathode assembly 1. When the switch arm of switch 33 is thrown to the left from the position shown in Fig. 3, the voltage from battery 27' as dropped by potentiometer 26 passes through the selected resistance 3t 31 or 32 and is impressed across the anode and cathode assembly 1;, which is mounted on a small animals skull as previously described. In this position of switch 38, called the maintain position, the proper voltage is maintained when it is not desired to take a galvanometer reading and eliminates any current build up period. In the position of the arm of switch 38, as shown in Fig. 3, conductor 40 is then connected by means of a conductor 42 in series with either of resistances 43, or 44, or directly to the arm of a three position switch 45 serially connected by means of a conductor 47 to the arm of a three position switch 48. The switch 48 can cut out either a resistance 49 or resistances 49 and 50, which are connected in series with a resistance 51. The reistances 49, 50 and 51 are connected in shunt between conductors 52 and 53 across a galvanometer 55 which preferably is of the automatic recording type. With a galvanometer having an internal resistance of 1950 ohms resistances 43 and 4A are of 34,500 and 5950 ohms respectively and resistances 49, 50 and 51 are 24,000, 12,000 and 12,000 ohms resistance respectively. The resistance in the circuit is adjustable so that the full scale deflection of the galvanometer can be adjusted for three different current values or sensitivities depending on the maximum current in microamperes to be recorded. Switches 35, 45 and 48 are ganged to be simultaneously operated by a common control and such that the same resistance is in circuit when switch 38 is in either the maintain or read position for the same galvanometer sensitivity setting. The circuit disclosed in Fig. 3 is per se the same as that employed in prior art by Clark and his coworkers.

In use, the small animal may be placed in a centrifuge and a predetermined acceleration force applied to the animal in terms of gravity units which will affect the oxygen content in the brain tissue and hence vary the potential drop and the current flowing between the anode block 2 and cathode wire 14, which form a current conduction path through the animals brain tissue. The variation in current will produce a visible output on the recording galvanometer 55. In the manner as described, in WADC Technical Rep 57-570 the data obtained from the recording galvanometer 55 may be interpreted as a measure of the oxygen availability vs. time while the animal is Subjected to the external acceleration forces. In like manner the animal may be placed in a chamber in which the pressure and temperature may be varied to simulate the effects of altitude and the variation in availability of oxygen in the brain tissue under such conditions is qualitatively determined. Due to the fact that the anode and cathode assembly in accordance with the invention creates no hazard of variation due to infection or displacement by the animal since it causes no apparent discomfort, the day-to-day reproducibility of data is insured and quantitative interpretations of the data have now become pos sible due to the stabilization of the entire system from the variable factors which heretofore have beset the prior art.

Having now described my invention I claim:

A concentric anode-cathode electrode adapted to be permanently implanted in the skull of a small animal for determining the availability of oxygen in the animals brain tissue comprising; a silver plated anode block, a cylindrical cavity formed in said anode block and having one open, a threaded extension on said block concentric with said cavity and having a small central passage therethrough connected at one end to said cylindrical cavity, an annular insulating sleeve positioned in said anode circular cavity, a plug of insulating material closing the bottom of said insulating sleeve, a metal cathode support mounted in said annular insulating sleeve, a platinum wire cathode electrode centrally secured in said cathode support and adapted to pass through said insulating plug and through said anode central passage to project beyond said anode block threaded extension said cathode wire being insulated throughout its length except at its tip portion from electrical contact with the anode, said anode block threaded extension being adapted to be screwed into a trephined hole in the animals skull, said cathode support, insulating means therefor and said 6 cathode Wire electrode being adapted to be inserted into said anode cylindrical cavity and said cathode wire projecting through said anode threaded extension into the brain tissue of the animal and means for removably securing the cathode support and insulating means therefor in the anode cylindrical cavity.

References Cited in the file of this patent UNITED STATES PATENTS 1,524,937 Keeler Feb. 3, 1925 1,898,209 Parker Feb. 21, 1933 2,437,697 Kalom Mar. 16, 1948 

